stronger BMX frame- cheap or expensive?

[HeadSmess]

The engine's shaft'll be sticking out the left side. Otherwise it would be spinning backwards (unless I drive it off the fan side of the crank)

I'm contemplating making a custom frame with thick (like 3/8" thick) wall pipes, but getting all the parts aligned and mitered properly would be a huge pain. 1mm change in the position of the headtube and the angle is affected by a lot of degrees, and any side to side misalignment and the headtube is being twisted side to side too

what im saying, is on the right hand side will be a gear on the crank, and a gear on the clutch... and the clutch will spin in reverse to the crank... (if its a standard sort of "clutch on primaryshaft" engine) and its usually around a 4:1 redux... so what if you had a chain from km48 to clutch on the right hand side? it does remove a shaft, bearings,unnecessary weight...and a big empty crankcase! space is at a premium on this build!

with km48 on left, shaft rotates the same way as crank. km 48 shaft on right, it will spin same way as primary shaft. crank becomes obsolete, ja?

add more redux, less wear on box and able to run smaller rear sprockets on wheel...

oil? is the magneto a dry or submerged type? the one on the moto engine...might be an issue with holes if its a wet type. the box will need oil still. why not use that magneto anyway? oh. no spark...meh. could be anything!

anyways, from the other side of the world all i can do is imagine really, so ignore me

cannabalise a bike. you want forks, headtube n bearings, (a BB?), the dropouts you can make...

get a flat bench. set up a frame you like on it so chain stay is parallel with it. start measuring heights etc to critical components with a square.

cut up some 4x2. (haaardwood) drill, nail, screw, glue... be careful and it will be correct? the stuffs good enough for houses, bridges, guitars and pianos... its good enough for a one off jig! brazing, working progressively, there wont be any warping... so what if you forget about how to pull the frame off afterwards? just smash the jig!

copy everything. as long as the headtube is square with the dropouts...the thing will be straight. using a jig, all you can blame is the jig maker!

i only suggest it as i know exactly what its like trying to line things up, hold them still, and then having it all crash down because the dog sat on the earth lead or something... and pushy frames are notoriously awkward!


you dont need any tubing thicker than 1.6mm! just gusset all corners and engine mounts. go look at the frame on a big 1000cc bike... triangulate, and all triangles should touch at the apex for max strength... (find some curved stuff and make the frame in the rotor shape!)


its going to be a lot of work in any case. have fun!

now why do i have to live next to a scottish person? one with bagpipes? arrrgh!


gone

 

[IbedaYank]

mitering tubes is easy... grinder and a few files

http://metalgeek.com/static/cope.pcgi

print it out wrap around tube.. trace pattern on pipe grind and file to line... so easy even I can do it...

 

[keatonx]

what im saying, is on the right hand side will be a gear on the crank, and a gear on the clutch... and the clutch will spin in reverse to the crank... (if its a standard sort of "clutch on primaryshaft" engine) and its usually around a 4:1 redux... so what if you had a chain from km48 to clutch on the right hand side? it does remove a shaft, bearings,unnecessary weight...and a big empty crankcase! space is at a premium on this build!

with km48 on left, shaft rotates the same way as crank. km 48 shaft on right, it will spin same way as primary shaft. crank becomes obsolete, ja?

add more redux, less wear on box and able to run smaller rear sprockets on wheel...

oil? is the magneto a dry or submerged type? the one on the moto engine...might be an issue with holes if its a wet type. the box will need oil still. why not use that magneto anyway? oh. no spark...meh. could be anything!

anyways, from the other side of the world all i can do is imagine really, so ignore me

cannabalise a bike. you want forks, headtube n bearings, (a BB?), the dropouts you can make...

get a flat bench. set up a frame you like on it so chain stay is parallel with it. start measuring heights etc to critical components with a square.

cut up some 4x2. (haaardwood) drill, nail, screw, glue... be careful and it will be correct? the stuffs good enough for houses, bridges, guitars and pianos... its good enough for a one off jig! brazing, working progressively, there wont be any warping... so what if you forget about how to pull the frame off afterwards? just smash the jig!

copy everything. as long as the headtube is square with the dropouts...the thing will be straight. using a jig, all you can blame is the jig maker!

i only suggest it as i know exactly what its like trying to line things up, hold them still, and then having it all crash down because the dog sat on the earth lead or something... and pushy frames are notoriously awkward!


you dont need any tubing thicker than 1.6mm! just gusset all corners and engine mounts. go look at the frame on a big 1000cc bike... triangulate, and all triangles should touch at the apex for max strength... (find some curved stuff and make the frame in the rotor shape!)


its going to be a lot of work in any case. have fun!

now why do i have to live next to a scottish person? one with bagpipes? arrrgh!


gone

Ohh, I think I get it, your thinking about me putting the sprocket on the clutch basket?
That could work, but wouldn't it get in the way of my clutch cover, so I wouldn't be able to disengage my clutch (mechanism is on cover) or fill the box with lube? Also, wouldn't it be a huge pain to get that big sprocket attached to the aluminum clutch basket?

And it would only save space front-to-back (I've got tons), and to do that I'd need to saw off the front part of the case, and therefore my front mounting hole.

Good idea with the wood jig; I could get all my angles set with
The miter saw. maybe I could get out the router and make a groove in the 2 by 4's for the pipes to sit in???

 

[keatonx]

I'm not using the case's ignition because-
It had no CDI, and finding a 4 stroke CDI with the same trigger point would be impossible
I needed to remove the flywheel, and therefore the magnets
It would have a 2 stroke timing curve
And I wouldn't be able to asjust timing on the fly.

 

[HeadSmess]

mitering tubes is easy... grinder and a few files

http://metalgeek.com/static/cope.pcgi

print it out wrap around tube.. trace pattern on pipe grind and file to line... so easy even I can do it...

for once, a genuine thankyou. i was trying to find that link a while ago... unfortunately its not so helpful for making intersections


yep, tis easy. just requires determination.